/*

Burrows–Wheeler Transform.

The code in this file is based on TheUnarchiver.
See README.md and docs/licenses/TheUnarchiver.txt for more information.

Copyright (C) 2019, Guillaume Gonnet

This program is free software: you can redistribute it and/or modify it under
the terms of the GNU General Public License as published by the Free Software
Foundation, either version 3 of the License, or (at your option) any later
version.

This program is distributed in the hope that it will be useful, but WITHOUT ANY
WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A
PARTICULAR PURPOSE.  See the GNU General Public License for more details.

You should have received a copy of the GNU General Public License along with
this program.  If not, see <https://www.gnu.org/licenses/>.

*/

#include "stuffit/utils/bwt.h"

namespace maconv {
namespace stuffit {



// Calculate inverse of BWT.
void CalculateInverseBWT(uint32_t *transform, uint8_t *block, int block_len)
{
    int counts[256] = {0};
    int cumulative_counts[256];
    
    for (int i = 0; i < block_len; i++)
        counts[block[i]]++;
    
    for (int i = 0, total = 0; i < 256; i++) {
        cumulative_counts[i] = total;
        total += counts[i];
        counts[i] = 0;
    }

    for (int i = 0; i < block_len; i++) {
        transform[cumulative_counts[block[i]] + counts[block[i]]] = i;
        counts[block[i]]++;
    }
}



// Reset the decoder.
void MtfDecoder::ResetDecoder()
{
    for (int i = 0; i < 256; i++)
        table[i] = i;
}


// Decode the next symbol.
int MtfDecoder::Decode(int symbol)
{
    int res = table[symbol];
    for (int i = symbol; i > 0; i--)
        table[i] = table[i-1];
    
    table[0] = res;
    return res;
}



} // namespace stuffit
} // namespace maconv